Bishop Fox cybersecurity researchers have discovered a critical security flaw in approximately 4,500 SonicWall firewalls that are exposed to the Internet as a result of a critical security breach. The flaw, CVE-2024-53704, is a high-severity authentication bypass vulnerability within SonicOS SSLVPN. Threat actors could exploit this flaw to gain unauthorized access to your VPN sessions, compromising the privacy of your sensitive data and the security of your network. 

SonicWall has issued a patch to address this issue, but unpatched systems remain at immediate risk. Due to this discovery, it is imperative that organizations relying on SonicWall firewalls immediately update those firewalls to mitigate the threat of cyberattacks leveraging this exploit and mitigate the amount of damage they will incur.

In its security bulletin dated January 7, 2025, SonicWall issued a warning about the high likelihood of an exploit resulting from a recently identified authentication bypass vulnerability within its SonicOS SSLVPN application that has been released to alert customers. There was a strong recommendation the company sent out to administrators to upgrade their SonicOS firewall firmware immediately so that they could mitigate the risk of unauthorized access and potentially dangerous cyberattacks. 

The SonicWall security company sent an email notification to all its customers about this critical vulnerability. In the email warning, SonicWall reiterated that the vulnerability poses an immediate threat to organizations that have SSL VPNs or SSH management enabled in their systems. This vendor stressed the importance of immediately updating firmware to protect networks and prevent malicious actors from exploiting them. 

In the latest research, SonicWall's SonicOS SSLVPN application was discovered to have an authentication bypass vulnerability, which has been rated at high risk with a CVSS score of 8.2. In this particular case, the problem affects several versions of SonicOS, specifically versions 7.1.x (all versions up to 7.1.1-7058), 7.1.2-7019, and 8.0.0-8035, which are widely utilized across both Generation 6 and Generation 7 SonicWall firewalls. 

Bishop Fox's cybersecurity team performed a thorough analysis of the vulnerability and successfully demonstrated exploitation scenarios to demonstrate the possibility of unauthenticated, remote attackers bypassing security mechanisms and hijacking active VPN sessions if they can bypass authentication mechanisms. To exploit this vulnerability, a specially crafted session cookie is sent to the SSL VPN endpoint's endpoint (/cgi-bin/sslvpnclient) that contains a base64-encoded string of null bytes. 

The misuse of this method can allow threat actors to gain access to authenticated VPN sessions without requiring valid credentials from the users, which poses a significant risk to organizations that use SonicWall firewall products as part of their security measures. The Cyber Security Research Lab has determined that as of February 7, 2025, approximately 4,500 SonicWall SSL VPN servers that connect to the internet remain unpatched and are vulnerable to exploitation by hackers. 

Initially, SonicWall published a security advisory on January 7, 2025, urging organizations to immediately update their firewall firmware to mitigate the risks associated with this high-severity vulnerability that allows authentication bypass. Several SonicOS firewall applications, which are affected by this flaw, have had firmware patches issued to address the problem. These include SonicOS 6.5.5.1-6n or later for Gen 6 firewalls, SonicOS 7.1.3-7015 or later for Gen 7 firewalls, and SonicOS 8.0.0-8037 or later for TZ80 firewalls, which have all been updated with these firmware patches. 

To mitigate the risks associated with these updates, organizations unable to implement these updates are strongly recommended to temporarily disable SSL VPN access or to restrict it only to trusted IP addresses. Despite the simplicity of the exploit, the risk it poses to corporate networks is significant; this is because it opens the door for widespread abuse from threat actors seeking to gain access to corporate networks to espionage, data exfiltration, or ransomware attacks. 

As soon as an adversary is inside a compromised environment, they will be able to escalate privileges, perform lateral movements, and further infiltrate critical systems. To combat these threats, administrators must immediately implement several key security measures that can help prevent these threats from happening. 

Too achieve this, all affected devices need to be updated with the latest firmware, SSL VPN and SSH management access should be restricted to trusted IP ranges, firewall logs should be monitored for anomalies, such as repeat session terminations or unauthorized login attempts, and multi-factor authentication (MFA) should be implemented on all devices. 

MFA, while ineffective in combating this specific exploit, remains a critical security measure that can be used against other types of cyberattacks as well. Since the risks associated with active exploitation are high, organizations should prioritize the security of their SonicWall firewalls to prevent unauthorized access to their networks, possible data breaches, and long-term network compromises.